区块链技术与应用详解

区块链技术采用以下三种手段保障安全与信任：

Block chain technology provides security and confidence by three means:

按线性时间顺序存储，即新区块总是追加至区块链尾部。截至2020年4月18日20:36，比特币区块链区块高度已超过626548。

stores in linear chronological order , i.e., new blocks are always added to the end of the block chain. As of 18 April 2020, the height of the Bitcoin block chain was more than 626548.

提升篡改、删除区块内容的难度，每个区块均包含自身及其前一个区块的哈希值。一旦某个区块内容被篡改，将导致后续所有区块的哈希值发生变化。黑客要掩饰这种改动，必须重新计算这些区块的哈希值，代价高昂，同时也因为每个区块在区块链网络中具有唯一高度，删除某一区块的操作变得几乎不可能。

increases the difficulty of tampering with and removing the content of blocks , each of which contains its own Hashi value and that of the previous block. Once the content of a block is tampered with, it will lead to a subsequent change in the Hashi value of all blocks. To disguise this change, hackers have to recalculate the Hashi value of these blocks at a high cost, and because each block has its only height in the network of blocks, it becomes almost impossible to delete a block.

共识模型验证，区块链网络要求用户计算机解决复杂数学问题以证明自身资质，当某计算机成功解决问题，便有权向区块链中添加新区块。然而，直至2020年4月，比特币网络中解决这类问题的概率仅为约15.5万亿分之一，为此，计算机需耗费大量电力运行相应程序。

The consensus model validates that the network of blocks requires user computers to solve complex mathematical problems to prove their qualifications, and that when a computer successfully solves problems, it has the right to add new blocks to the chain of blocks. However, as of April 2020, the probability of resolving such problems in the Bitcoin network is only about one-fifth trillion, for which the computer will have to run the corresponding programs with a large amount of electricity.

工作量证明（Proof of Work，PoW）是众多加密货币的基础机制，它构建了一个系统，要求参与者付出一定但可实施的努力来防止滥用计算资源。

Workload certification (Proof of Work, PoW) is the foundation mechanism for numerous encrypted currencies, and it builds a system that requires participants to make certain but implementable efforts to prevent misuse of computing resources.

为一组比特币交易生成随机哈希值对现代计算机来说非常简单，于是，为使之成为一个更加实质性的任务，比特币网络设置了难度级别，即设定目标值（target）。目标值越低，生成有效哈希值的范围就越小，相应生成难度越大。矿工们通过调整一个一次性使用的整数（nonce）以改变输入数据，找到一个符合目标值的有效哈希值后，会将其广播至网络，并将区块添加至区块链，而成功找到nonce整数的矿工会获得相应的加密货币奖励，这个nonce整数即为需解决的数学难题。

By adjusting a one-time integer (nonce) to change input data, by finding an effective Hashi value that meets the target value, the miners will broadcast it to the network and add blocks to the block chain, and by successfully finding an entire number of nónce, which will be given a corresponding encryptive monetary incentive.

双重支付（Double-Spending）是指用同一笔数字货币进行两次消费，这是加密货币面临的核心安全挑战。比特币之所以长久屹立并深受推崇，正是因为成功解决了这个问题。

Double-paying, which means spending twice in the same digital currency, is a central security challenge for encrypted money. Bitcoin’s persistence and popularity is due to its success.

以现实生活中的星巴克购咖啡为例，顾客支付现金50元后，店员立刻确认并交付商品，这笔交易即告完成，顾客无法再次使用这50元。而在微信或支付宝支付场景下，账户余额减少，两次交易无法同时扣除相同金额，因为银联系统会确保第二笔交易建立在第一笔交易完成基础上。

In a real-life case, Starbucks buys coffee, and once the customer pays 50 dollars in cash, the shopkeeper confirms and delivers the merchandise, and the transaction is completed, and the customer cannot use it again. In the context of the micro-mail or payment of the treasure, the balance of the account is reduced, and the same amount cannot be deducted from both transactions, because the second transaction will be based on the completion of the first transaction.

但在比特币等数字货币领域，初期账户中并无Coin，需要通过挖矿获取。币种的去中心化特性使得Coin无法集中存储，私钥仅能提取和消费属于自己的Coin，一旦私钥丢失，对应的Coin（包括自己的和其他人的）将永久失去。

In digital currency such as Bitcoin, however, there is no Coin in the initial account, which needs to be obtained through mining. The decentralized nature of the currency prevents Coin from centralizing, the private key can only be extracted and consumed by its own Coin, and the corresponding Coin (including its own and others) will be permanently lost once the private key is lost.

比特币如何防范双重支付呢？举个场景：买家使用私钥对其持有的1个比特币进行签名后，分别向卖家A和卖家B的公开地址发出交易请求，两位卖家各自用自己的私钥确认交易，这两笔交易随后进入待确认池等待矿工审核。通常情况下，第一笔交易会被矿工确认并加入下一个区块，而第二笔交易则被视为无效并从网络中剔除。然而，由于网络存在延迟，两个交易可能同时被不同矿工选取进行确认。这时，获得最多确认数的交易将会被写入区块链，而另一笔交易将被废弃。在这种情况下，卖家A可能无法获得Coin，利益受损。

How does Bitcoin protect against double payment? A scenario: When a buyer signs a bitcoin held by a private key, it sends a request for a transaction to the public address of Vendor A and Vendor B, respectively, and the two sellers each confirm the transaction with their own private key, which then enters the confirmed pool for verification by the miners. Normally, the first transaction will be confirmed by the miners and added to the next block, while the second transaction will be considered null and void and rejected from the network. However, due to a delay in the network, two transactions may be identified by different miners at the same time.

解决之道在于，卖家应当等待至少6次确认。这意味着一笔交易被写入区块链后，接下来还有6个包含其他交易的新区块被添加。每个区块及其所包含的交易皆与之前的区块相关联（基于哈希值）。攻击者若想逆转最近6个区块内的所有交易以实现双重支付，在计算层面上几乎是不可能的任务。当卖家收到6次确认后，即可确信该笔交易并非源自试图进行双重支付的买家。

The solution is that the seller should wait for confirmation at least six times. This means that when a transaction is written into the block chain, six new blocks containing other transactions are added. Each block and the transactions it contains are linked to the previous block (based on the Hashi value). If the attackers want to reverse all transactions in the last six blocks to achieve double payment, it is almost impossible at the computing level.

优点：

Advantages:

通过剔除人工验证环节提高准确性。

Improve accuracy by removing manual validation.

去除第三方验证环节，降低交易成本。

Remove third-party certification and reduce transaction costs.

去中心化设计使篡改更为困难。

Decentralizing the design makes tampering more difficult.

交易安全、私密且高效。

Transactions are safe, private and efficient.

缺点：

Disadvantages:

挖矿相关的技术成本高昂。

The technology associated with mining is costly.

处理每秒交易数量较低，比特币网络大约每10分钟生成一个区块，每个区块平均包含约3000笔交易。

The number of transactions processed per second is low, and the Bitcoin network generates about one block every 10 minutes, with an average of about 3,000 transactions per block.

私密性可能导致被用于非法行为。

Privacy may lead to the use of illegal acts.

易受黑客攻击风险。

Be at risk of hacking.

加密数字货币，如比特币。

Encrypted digital currency , e.g. Bitcoin.

医疗记录管理，医疗机构可利用区块链安全存储患者的医疗记录，生成并签署病历时将其写入区块链，确保记录无法篡改并提供信息凭证。个人健康记录可以用私钥加密并存储于区块链上，保证只有授权人士才能访问，确保隐私安全。

Medical records management . Medical institutions can use the block chain to store patients’ medical records safely, to generate and sign medical records and to include them in the block chain, to ensure that records cannot be tampered with and to provide proof of information.

内容分发，运用区块链上的智能合约（Smart Contract），革新传统内容分发模式，确保权利人持续获得收益。

is distributed , using smart contracts on block chains (Smart Contract) to innovate traditional content distribution models to ensure that rights holders continue to reap benefits.

供应链管理，供应商可利用区块链记录原材料采购源头，下游企业借此可验证产品真实性。目前，食品等行业借助区块链追溯食品安全及流向，从

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